The term Direct Write is commonly used to describe a range of technologies which allows the fabrication of two or three-dimensional functional structures using processes that are compatible with being carried out directly onto potentially large complex shapes (DTI Report February 2004 “Direct Writing”). Direct Write manufacturing techniques include: Ink jet, Micro-spray, Quill, Pen, Aerosol, Pulsed laser evaporation, and Laser direct etching. Direct Write has the ability to fabricate active and passive functional devices directly onto structural parts and assemblies. The benefits of utilizing these techniques are increased functionality, reduced size and weight, reduced cost, design simplification, reduction in component number and a reduction in time to market. In the field of Aerospace, there are applications for Direct Write such as electronic circuits, sensors, RF devices, displays, stealth materials, meta-materials, packaging, sensors and harnesses.
Additive manufacturing is a generic term used to describe a process by which successive layers of a structure, device or mechanism are formed, and in which in each layer components such as electrical circuit components may be formed by a Direct Write method. The term “additive” is used to contrast conventional manufacturing processes such as lithography, milling, turning etc, in which material from a solid layer or object is taken away or removed.
In general, in Direct Write and additive manufacturing processes, writing or printing materials are referred to as inks, although the actual form of the material may comprise a wide range of powders, suspensions, plasters, colloids, solutes, vapors etc, which may be capable of fluid flow and which may be applied in pastes, gels, sprays, aerosols, liquid droplets, liquid flows, etc. Once applied, the material may be fixed by curing, consolidating, sintering or allowing to dry, frequently involving application of heat to change the state of the material to a solid phase. For the purposes of the present specification, the term “Direct Write ink” is intended to cover all such materials.
The object or structure (which may be a very large three-dimensional object) on which the deposition is performed is referred to in the art by the term “substrate”, and this is the sense of the term as used in the present specification. The deposited ink, once fixed on the substrate; forms a component or part of a structure that is to be manufactured.
With almost all deposition methods used for Direct Write, after deposition the inks have to be cured, consolidated or sintered. There are inks for which this can be done with optical radiation but for most high performance inks this is done thermally by placing the substrate in an oven. This method has numerous deficiencies:                Curing temperature for the inks is limited by the substrate operating temperature. Generally the higher the temperature at which the inks are cured, the better the performance. Thus curing at a lower temperature limited by the substrate compromises the ink performance, and limits the range of ink chemistries that can be used.        There may be other elements on the substrate whose performance would be impaired by the elevated temperature they would be exposed to during a curing cycle.        If the substrate is large it may not be practical to place it in the oven for curing.        Invariably, printing requires multiple layers of printing and generally each layer has to be thermally consolidated prior to the deposition of the subsequent layer. If this is done by placing the substrate in the oven after each layer is printed, then there can be problems in registration accuracy when the substrate is tooled for printing. Ensuring accurate registration after each curing step in the oven also requires complex and costly tooling.        When depositing multiple layers, the removal and subsequent realignment of the substrate for curing in the oven is a costly and time consuming step.        
US-A-2005/0015175 and US-A-6405095 mention the possibility, among other possibilities, of using an induction coil to effect fixing.
The present invention aims to overcome or at least substantially reduce some of the above discussed drawbacks.